1. Field of the Invention
The present invention relates to a ferrite toroidal core in an annular trough having a winding applied around the trough.
2. Description of the Prior Art
Wound ferrite toroidal cores which are used, for instance, in toroidal core inductors and transformers are provided with an envelope of casting resin or of thermoplastic synthetic resin. When the resin envelope is applied, a pressure caused by the shrinkage of the resin as it hardens on the ferrite toroidal core potentially causes destruction or at least a considerable deterioration of the electrical and magnetic properties of the ferrite toroidal core. This is assuming that the ferrite core has inadequate protection.
As a protection means for the ferrite toroidal core, a trough member has been developed having an annular shape and closed by a cap, the trough member being formed of thermoplastic material. Over and above this, it has been proposed to protect the ferrite toroidal core with a coating of wax or a similar material, thus providing a buffer between the bare ferrite core and the resin envelope to provide a barrier for the shrinkage forces exerted by the envelope during hardening.
A technique known as "soft casting" has been created for the resin envelope. However, soft casting does not provide an adequately tight envelope and, consequently, leads to a decrease in the insulation value of the envelope such as when the wound core is stored in a damp area.